1. Field of the Invention
The present invention relates a method of fabricating a liquid crystal display (LCD), and more particularly, to a method of fabricating a liquid crystal on silicon (LCOS) display panel.
2. Description of the Prior Art
In modern planar display technology, plasma display panels (PDPs) and liquid crystal displays (LCDs) are popular choices. They both constitute numerous display grids called pixel cells. The former one is applied in a large-sized market and still has not reached widespread acceptance since the technique for mass production has still not been perfected and cost is high. A thin-film transistor LCD (TFT LCD), which has prevailed in recent years, is representative of the latter one and is mainly applied in the market smaller than 30 inches. During the fabrication of the TFT LCD products, however, defects such as dots or lines may occur on the LCD. Thus, compensative techniques are required to improve the production yields.
A liquid crystal on silicon (LCOS) display utilizes a silicon chip as a substrate and utilizes a standard CMOS process to form pixel cell matrices, integrated drivers, and other electronic devices on the silicon chip. An advantage of the LCOS display is its utilization of the CMOS process, since the CMOS process is well developed in the present semiconductor industry. As a result, high stability and reliability can be achieved when compared to the LCD. In addition, using this process, each pixel pitch can be shrunk to less than 10 μm, therefore high resolutions are obtained. When compared to the PDP, the LCOS display not only has an absolute superiority in cost but also has intrinsic advantages of the LCD. In addition, being assisted with adequate projection techniques, the LCOS display can further be applied in markets for large-sized displays. Therefore, the liquid crystal on silicon display attracts many major manufacturers to devote themselves to development, and is the display with the highest potential.
Please refer to FIG. 1 to FIG. 3 of schematic diagrams of a conventional method of fabricating a liquid crystal on silicon (LCOS) display panel 10. As shown in FIG. 1, the LCOS display panel 10 comprises a silicon substrate 12. An active region 14 is disposed on the silicon substrate 12. The active region 14 comprises a control circuit (not shown) and a plurality of electrodes 16, which is electrically connected to the control circuit, positioned on the surface of the active region 14. The control circuit comprises a plurality of transistors, such as CMOS transistors, arranged in a matrix form to drive the electrodes 16.
As shown in FIG. 2, an alignment film 18 is coated on the silicon substrate 12. After that, a rubbing process is then performed to form a plurality of alignment trenches by using a rubbing cloth to rub the surface of the alignment film 18.
As shown in FIG. 3, a transparent conductive layer 20, which is composed of materials with high transparence and conductivity such as indium tin oxide (ITO), is added to the silicon substrate 12. A glass substrate 22 is put on the transparent conductive layer 20 and a cell gap is left between the transparent conductive layer 20 and the silicon substrate 12. Then, a liquid crystal filling process is performed to fill the cell gap with liquid crystal so that a liquid crystal layer 24 is formed.
A liquid crystal alignment process is performed at last. The liquid crystal alignment process is used to make the liquid crystal molecules in the liquid crystal layer 24 have a predetermined tilt direction. Normally, the liquid crystal molecules in the liquid crystal layer 24 will rotate when an electric field is applied thereon. After forming this predetermined tilt direction, the liquid crystal molecules tend to rotate along the same direction, which is the predetermined tilt direction, and therefore, the liquid crystal molecules can be aligned more uniformly and the contrast of the display panel 10 can be improved. In the conventional method of fabricating an LCOS display panel, the alignment process is performed with a plurality of aligned trenches disposed on the bottom of the liquid crystal layer 24. In addition, another well-known alignment process is a polymer stabilization process. In this process, liquid crystal molecules are mixed with monomers before filling into the display panel 10 and an electric field is applied thereon so that the liquid crystal molecules and the monomers are twisted along a predetermined direction according to the direction of the electric field. Then, a curing process is performed under UV light radiation while the electric field remains. Therefore, the monomers are cured and combined to form a polymer network with the predetermined direction, which is the predetermined tile direction of the liquid crystal layer 24. Therefore, when the liquid crystal molecules in the liquid crystal layer 24 are twisted due to an electric field, the liquid crystal molecules tend to rotate along the predetermined tilt direction and therefore a better display performance is obtained.
The conventional method of fabricating the LCOS display panel is using a rubbing process to form a plurality of aligned trenches and using an external electric field to control the predetermined tilt direction of the liquid crystal molecules. Thus, when an electric field is applied to the LCOS display panel, the liquid crystal molecules rotate along the predetermined tilt direction. However, the rubbing process often damages electrical circuit parts disposed on the active region 14 on the silicon substrate 12 so that the reliability of products is deteriorated and the yield is affected. In addition, as sizes of pixels shrink, the trenches or extrusions disposed on the electrodes or between the electrodes interfere with the uniformity of the electric field. Thus, when the electric field is applied to perform the polymer stabilization process for aligning the liquid crystal molecules, the electric field is interfered and the local electric field near the electrodes is irregular. Therefore, the predetermined tilt direction of the liquid crystal molecules is irregular and the display performance is thereby decreased.